> I thought the OP said that lwindow doesn't work for him _without_
> redefining it.  IOW, the default action of the key is somehow
> intercepted by Emacs when it shouldn't be.
>
> Am I confused?

No, you're right and I was. I misunderstood.

But then, he says "Iwindow key with the default setting(nil)". But w32-pass-lwindow-to-system's default value is t, both in 26.2 and 27.0.50.

So I'm still confused.